The Natural Cycles application is an FDA-cleared birth control and fertility tracking tool that relies on daily data input to determine a user’s fertility status. The app uses an algorithm to analyze basal body temperature, which typically rises after ovulation, along with other cycle data. Logging menstruation is a foundational data point, as the first day of flow marks the start of a new menstrual cycle, known as Cycle Day 1 (CD1). This data, combined with temperature readings, provides a personalized prediction of the fertile window and subsequent cycle length.
Step-by-Step Guide to Logging Menstruation
To log your period flow, navigate to the data entry screen, typically accessed by tapping the plus icon (+) or opening the daily “Add Data” page. Locate the “Bleeding” or “Period” section, which is separate from the temperature entry field. The app provides different options for logging the type of bleeding you are experiencing.
Select the “Period” option to signal the algorithm that a new cycle has begun. The app allows you to specify the flow intensity for that day, usually categorized as light, medium, or heavy. You must repeat this logging process for every subsequent day of your flow, ensuring the algorithm accurately tracks the duration of your menses. You can also log period data for past days by selecting a previous date on the calendar.
Understanding Bleeding Types and Logging Nuances
Accurately logging your period requires distinguishing between true menstrual flow and light spotting. The algorithm uses the “Period” log to start a new cycle, while “Spotting” is a secondary tracker that does not impact fertility status calculation. True period flow should be logged when bleeding requires the use of a pad or tampon, even if the flow is initially light.
Spotting is very light bleeding, often brown or pink, that is only visible on toilet paper or requires a panty liner at most. If light bleeding occurs at the beginning of your flow, it should be logged as “Period” to correctly establish Cycle Day 1. Any light bleeding at the end of your menses should continue to be logged as “Period” until the bleeding completely stops. If you have recently stopped hormonal birth control, your initial bleed must be logged as “Withdrawal bleeding,” which is distinct from a true period because it is not triggered by ovulation.
How Logging Impacts Your Fertility Status
Logging the first day of your period affects the Natural Cycles algorithm by resetting the cycle count. The app uses this start date to calculate the predicted length of your current cycle based on historical data. This new cycle immediately initiates the pre-ovulatory (follicular) phase, where the algorithm is cautious about fertility.
Logging your period often results in the app displaying a Red Day, indicating potential fertility and the need for protection. Although bleeding confirms no pregnancy occurred in the previous cycle, the algorithm defaults to Red Days early on until it confirms safety using temperature and historical cycle patterns. The first day of the period establishes the baseline for the upcoming fertile window prediction.
The algorithm requires multiple data points, including a sustained temperature rise, to confirm that ovulation has occurred and the fertile window has closed. Until this post-ovulatory temperature rise is detected, the algorithm relies on the logged period start date to predict the earliest possible day for the next ovulation. Consistent and accurate logging allows the algorithm to learn your cycle patterns, which often results in an increased number of Green Days (non-fertile) over time.